Association of in utero HIV exposure with child brain structure and language development: a South African birth cohort study

Background There is a growing population of children with in utero HIV exposure who are at risk of poor neurodevelopmental outcomes despite avoiding HIV infection. However, the underlying neurobiological pathways are not understood and neuroimaging studies are lacking. We aimed to investigate the cortical brain structure of children who are HIV-exposed and uninfected (HEU) compared to HIV-unexposed (HU) children and to examine the relationship with neurodevelopment. Methods The Drakenstein Child Health birth cohort study enrolled pregnant women from a high HIV prevalence area in South Africa with longitudinal follow-up of mother–child pairs. High-resolution magnetic resonance imaging scans from 162 children (70 HEU; 92 HU) were acquired at 2–3 years of age. All HEU children were born to mothers taking antiretroviral therapy. Measures of brain structure (cortical thickness and surface area) in the prefrontal cortex regions were extracted from T1-weighted images and compared between groups using multivariate analysis of variance and linear regression. Child development, assessed using the Bayley Scales of Infant and Toddler Development-III, was correlated with cortical structure, and mediation analyses were performed. Results Analyses demonstrated an association between HIV exposure and cortical thickness across the prefrontal cortex (p = 0.035). Children who were HEU had thicker cortices in prefrontal regions, with significantly greater cortical thickness in the medial orbitofrontal cortex (mOFC) bilaterally compared to HU children (3.21 mm versus 3.14 mm, p = 0.009, adjusted effect size 0.44 [95% CI 0.12 to 0.75]). Estimates held across multiple sensitivity analyses. There were no group differences in cortical surface area. Language scores, which were lower in HEU versus HU children (81.82 versus 86.25, p = 0.011, effect size − 0.44 [95% CI − 0.78 to − 0.09]), negatively correlated with prefrontal cortical thickness in both groups. Cortical thickness in the mOFC mediated the relationship between HIV exposure and poor language outcomes (Sobel test p = 0.032). Conclusions In this cohort study, exposure to HIV during pregnancy was associated with altered cortical structure in early life. Our findings indicate that differences in cortical thickness development in the prefrontal region in children who are HEU may be a pathway leading to language impairment. Longitudinal studies are needed to determine the lasting impact. Supplementary Information The online version contains supplementary material available at 10.1186/s12916-024-03282-6.


Mediation Analyses
We performed a mediation analysis to evaluate whether, and to what extent, the effect of HIV exposure on language is mediated through cortical thickness -a hypothesis generated from findings in the prior analyses.Mediation analysis provides an estimation of the direct effect, indirect effect and total effect of HIV exposure (exposure) on language function (outcome), and whether the indirect effect is mediated by cortical thickness (mediator).We applied the Baron and Kenny (1986) approach that uses sequential regression analyses.The criteria for mediation are that there are associations between: (1) HIV exposure and language development (path c); (2) HIV exposure and cortical thickness (path a); (3) cortical thickness and language score (path b) controlling for the exposure; and that (4) the effect of HIV exposure on language function is lost (full mediation) or reduces (partial mediation) after controlling for cortical thickness (path c').Models were adjusted for potential confounding variables identified a priori.The percentage that the mediator contributed was calculated as the ratio of the indirect effect coefficient to the total effect coefficient (proportion of total effect mediated).A reduction of the direct effect coefficient after adjusting for the mediator was taken as evidence of mediation.We confirmed the findings using structural equation modelling.Summary: Estimates of the direct and indirect (mediated through brain structure) effect of HIV exposure on language development, measured by the BSID-III are shown.All scores were standardized.The total effect for HIV exposure on language development is -0.35.The direct effect for HIV exposure on language development is smaller than the total effect (-0.23).The indirect effect of HIV that passes through the mediator, mOFC thickness, is -0.12, which is statistically significant.The proportion of the total effect that is mediated is approximately one third (35%), and the ratio of the indirect effect:direct effect is approximately half the size of the direct effect (0.53).Similar results are obtained in unadjusted analyses, holding on bootstrapping with 1000 repetitions.Significance testing of indirect effect (adjusted, standardized) using the Sobel method showed mediation is complete (p=0.032).Similar results were obtained using the Monte Carlo test.Abbreviation: mOFC: medial orbitofrontal cortex

Table S1 : Comparison of study demographics of children with imaging versus those without imaging
Data are N(%), mean (SD).Continuous variables were compared with unpaired t-tests; categorical variables were compared with Chi-squared tests.#Full DCHS cohort excluding two children with HIV-infection.Percentages are cited among those with non-missing values.Missing data: birthweight (n=13); birth head circumference (n=23); maternal smoking (n=7); maternal alcohol use (n=146); breastfeeding (n=77). Footnote:

Table S3 : Adjusted mean differences in cortical thickness according to HIV exposure restricted to one site Cortical thickness, mean SD) Minimally adjusted model a Full adjusted model b
Footnote: Multiple linear regression estimates for HIV exposure on cortical thickness (mm) restricted to the clinic site where the majority of HEU children attend.*p<0•05 a Adjusted for child age and sex; b Adjusted for child age and sex, household income, maternal age and education.Cortical thickness (mean of left and right hemispheres), mean differences (regression coefficients minimally and fully adjusted in multiple regression models), p-values and effect sizes are presented.Effect sizes were calculated using Cohen's d with associated 95% confidence intervals.Residuals were assessed for each model using quantile-quantile plots and were normally distributed.A positive regression estimate indicates HIV exposure is associated with thicker cortices in that region.Abbreviations: HEU = children who are HIV-exposed and uninfected; HU = children who are HIV-unexposed.

Table S4 : Adjusted mean differences in cortical thickness according to HIV exposure restricting to HEU children born to mothers on the same first-line ART regimen Minimally adjusted model a Full adjusted model b
a Adjusted for child age and sex; b Adjusted for child age and sex, household income, maternal age and education.Cortical thickness (mean of left and right hemispheres), mean differences (regression coefficients minimally and fully adjusted in multiple regression models), p-values and effect sizes are presented.Effect sizes were calculated using Cohen's d with associated 95% confidence intervals.A positive regression estimate indicates HIV exposure is associated with thicker cortices in that region.Abbreviations: HEU = children who are HIV-exposed and uninfected.

Table S5 : Comparison of cognitive, language, and motor development between HEU and HU children
Footnote: Composite neurodevelopmental domain scores, mean differences (regression coefficients minimally and fully adjusted in multiple regression models), p-values and effect sizes for associations between neurodevelopment and HIV exposure.Supplementary table with raw scores below.a Adjusted for child age and sex; b Adjusted for child age and sex, household income, maternal age and education.*p<0•05.Effect sizes were calculated using Cohen's d with associated 95% confidence intervals.Residuals were assessed for each model using quantile-quantile plots and were normally distributed.A negative regression estimate indicates HIV exposure is associated with lower scores

Table S7 : Structural equation model
Covariates included in models: child age and sex, household income, maternal age and education Proportion of total effect mediated: indirect/total effect: 0.35 Ratio of indirect to direct effect: indirect/direct: 0.53 Ratio of total to direct effect: total/direct: 1.53 *